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But there is a problem with this calculation. The third line of the following table shows that the compound formed from hydrogen and oxygen is water, which is found tohave mass proportion 8:1 oxygen to hydrogen. Our expectation should then be that an oxygen atom mass is 8.0times a hydrogen atom mass. Thus the three measurements inthe following table appear to lead to contradictory expectations of atomic mass ratios. How are we toreconcile these results?

Mass relationships for hydrogen, nitrogen, oxygen compounds
Compound Total Mass Mass of Hydrogen Mass of Nitrogen Mass of Oxygen "Expected" Relative Atomic Mass of Hydrogen "Expected" Relative Atomic Mass of Nitrogen "Expected" Relative Atomic Mass of Oxygen
Nitric Oxide 15.0 g - 7.0 g 8.0 g - 7.0 8.0
Ammonia 8.5 g 1.5 g 7.0 g - 1.5 7.0 -
Water 9.0 g 1.0 g - 8.0 g 1.0 - 8.0

One possibility is that we were mistaken in assuming that there are atoms of the elements which combine to form the different compounds. If so, then we would not be surprised to see variations in relative masses of materials which combine.

Another possibility is that we have erred in our reasoning. Looking back, we see that we have to assume how many atoms of each type are contained in each compound to find the relative masses of the atoms. In each of the above examples, we assumed the ratio of atoms to be 1:1 in each compound. If there are atoms of the elements, then this assumption must be wrong, since it gives relative atomic masses which differ from compound to compound. How could we find the correct atomic ratios? It would help if we knew the ratio of the atomic masses: for example, if we knew that the oxygen to hydrogen mass ratio were 8:1, then we could conclude that the atomic ratio in water would be 1 oxygen and 1 hydrogen. Our reasoning seems to circular: to know the atomic masses, we must know the formula of the compound (the numbers of atoms of each type), but to know the formula we must know the masses.

Which of these possibilities is correct? Without further observations, we cannot say for certain whether matter is composed of atoms or not.

Observation 2: multiple mass ratios

Significant insight into the above problem is found by studying differentcompounds formed from the same elements. For example, there are actually three oxides of nitrogen, that is,compounds composed only of nitrogen and oxygen. For now, we will call them oxide A, oxide B, and oxideC. Oxide A has oxygen to nitrogen mass ratio 2.28 : 1. Oxide B has oxygen to nitrogen mass ratio 1.14 : 1,and oxide C has oxygen to nitrogen mass ratio 0.57 : 1.

The fact that there are three mass ratios might seem to contradict theLaw of Definite Proportions, which on the surface seems to say that there should be just oneratio. However, each mass combination gives rise to a completely unique chemical compound with verydifferent chemical properties. For example, oxide A is very toxic, whereas oxide C is used as ananesthesia. It is also true that the mass ratio is not arbitrary or continuously variable: we cannot pickjust any combination of masses in combining oxygen and nitrogen, rather we must obey one of only three. Sothere is no contradiction: we simply need to be careful with the Law of DefiniteProportions to say that each unique compound has a definite mass ratio of combining elements.

Questions & Answers

anyone know any internet site where one can find nanotechnology papers?
Damian Reply
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
characteristics of micro business
for teaching engĺish at school how nano technology help us
Do somebody tell me a best nano engineering book for beginners?
s. Reply
there is no specific books for beginners but there is book called principle of nanotechnology
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
what is the actual application of fullerenes nowadays?
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
is Bucky paper clear?
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Do you know which machine is used to that process?
how to fabricate graphene ink ?
for screen printed electrodes ?
What is lattice structure?
s. Reply
of graphene you mean?
or in general
in general
Graphene has a hexagonal structure
On having this app for quite a bit time, Haven't realised there's a chat room in it.
what is biological synthesis of nanoparticles
Sanket Reply
what's the easiest and fastest way to the synthesize AgNP?
Damian Reply
types of nano material
abeetha Reply
I start with an easy one. carbon nanotubes woven into a long filament like a string
many many of nanotubes
what is the k.e before it land
what is the function of carbon nanotubes?
I'm interested in nanotube
what is nanomaterials​ and their applications of sensors.
Ramkumar Reply
Berger describes sociologists as concerned with
Mueller Reply
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Source:  OpenStax, General chemistry i. OpenStax CNX. Jul 18, 2007 Download for free at http://cnx.org/content/col10263/1.3
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